1. Field of the Invention
The present invention relates to a hammer drill having a driving mode switching mechanism that switches the driving mode of a tool bit among a hammer mode in which the tool bit is caused to perform striking movement in its longitudinal direction, a drill mode in which the tool bit is caused to perform rotation on its axis and a hammer drill mode in which the tool bit is caused to perform striking movement and rotation.
2. Description of the Related Art
Japanese laid-open patent publication No. 2002-192481 discloses a hammer drill having a driving mode switching mechanism that switches among three modes as described above. The known hammer drill has a mode-change switching lever that is turned on a predetermined rotation axis by a user. When the switching lever is turned, a clutch of a striking force transmitting mechanism is switched between a power transmission state and a power transmission interrupted state via a first switching member that is activated by a first eccentric pin provided in the switching lever. Further, a clutch of a rotating force transmitting mechanism is switched between a power transmission state and a power transmission interrupted state via a second switching member that is activated by a second eccentric pin of the switching lever. With such a construction, a mechanism for switching the clutch for the striking movement and a mechanism for switching the clutch for rotation, which are activated by turning the switching lever, interfere with each other when the switching lever is turned over 180°. Therefore, with reference to a position for the hammer drill mode, the hammer mode is selected when the switching lever is turned clockwise by a predetermined angle. Further, when the switching lever is turned counterclockwise by a predetermined angle, the drill mode is selected.
However, with this known driving mode switching mechanism, mode change is performed by turning the switching lever in either direction with reference to the hammer drill mode position. Therefore, the hammer drill mode position is inevitably located between the hammer mode position and the drill mode position. In order to switch from the hammer mode to the drill mode or from the drill mode to the hammer mode, the switching lever must be turned through the hammer drill mode position and over 180°. Therefore, the known driving mode switching mechanism is desired to be further improved in ease of switching operation.